The present invention relates generally to a double row taper-roller bearing and an assembling method thereof, and more particularly to a method of assembling a double row taper-roller bearing by controlling a negative axial gap. The present invention also relates to a wheel support structure and a method of assembling the same structure.
In a conventional double row taper-roller bearing, the control of a negative axial (axial direction) gap has hitherto involved such a construction that two pieces of inner rings are disposed side by side on a cylindrical member facing to one single outer ring having two tapered track surfaces, and a spacer is interposed between two inner rings. More specifically, so to speak, two sets of completed taper-roller bearings are disposed side by side in the axial direction, the spacer is interposed therebetween, a pre-load is controlled by fastening the two bearings from the axial direction, and the double row taper-roller bearing is assembled.
The double row taper-roller bearing, however, tends to be a part of an apparatus using this type of bearing rather than a single unit of bearing, wherein an inner ring and an outer ring of the bearing are being made integral with the members which have supported so far the inner ring and the outer ring. For example, in the double row taper-roller bearing for the hub unit for fitting a wheel of an automobile, it has been proposed that the conventional inner ring and outer ring be united into one unit integral with a flanged member formed with a bolt hole, which has hitherto supported the inner ring and the outer ring and fixedly joined to the wheel or the car body.
What is proposed above is, however, unable to control in fact the negative axial gap and can be therefore neither assembled nor used.
FIG. 13 shows a double row taper-roller bearing 1 which has been broadly used so far for supporting the wheel. This double row taper-roller bearing 1 is constructed in such a way that a pair of inner rings 3, 3 are each so supported by a plurality of taper-rollers 4, 4 as to be rotatable on a minor-diameter side of one single outer ring 2. Double row outer ring tracks 5, 5 each taking a configuration of tapered concave surface are formed along an inner peripheral surface of the outer ring 2, and inner ring tracks 6, 6 each assuming a configuration of tapered convex surface are formed along outer peripheral surfaces of the respective inner rings 3, 3. The taper-rollers 4, 4 are sandwiched in between the outer ring tracks 5, 5 and the inner ring tracks 6, 6 in a state the rollers 4, 4 are so held by cages or holders 7, 7 as to be rollable. Further, combined seal rings 8, 8 are attached between an inner peripheral surface at two side ends of the outer ring 2 and outer peripheral surfaces of side ends of the inner rings 3, 3, thereby closing openings at two axial side ends of an air space 9 in which the taper-rollers 4, 4 are set.
The above-described double row taper-roller bearing 1, which has hitherto been widely used, is assembled in procedures shown in FIGS. 14 and 15. To be specific, at first, as shown in FIG. 14, the taper-rollers 4, 4 are arranged along circumferences of the inner rings 3, 3 in the state of being so held by the cages or holders 7, 7 as to be rollable. Then, the inner rings 3, 3 are inserted inside of the outer ring 2 while remaining in this state, and, as shown in FIG. 15, the taper-rollers 4, 4 are brought into contact with the outer ring tracks 5, 5 and the inner ring tracks 6, 6. Then, finally, the combined seal rings 8, 8 are attached between the outer peripheral surfaces of the side ends of the inner rings 3, 3 and the inner peripheral surface at the two side ends of the outer ring 2.
The double row taper-roller bearing 1 itself, which is shown in FIG. 13, has no particular problem. In recent years, however, for the purpose of reducing the number of assembly steps by decreasing the number of parts, a so-called third-generation hub unit structure has been contrived, wherein the double row taper-roller bearing for supporting the wheel is provided integrally with the hub for supporting and fixing the wheel. If this type of third-generation hub unit structure is adopted, a flange for supporting the wheel is provided on an outer peripheral surface of one side end of the hub body, and a first inner ring track taking a configuration of tapered convex surface and serving to configure the taper-roller bearing of the first row, is formed directly along an outer peripheral surface of an intermediate portion. Then, an inner ring, having a second inner ring track taking a configuration of tapered convex surface, for configuring the taper-roller bearing of the second row, is fixedly fitted to an outer portion of a small-diameter stepped portion formed on an outer peripheral surface of the other side end of the hub body.
In the case of this structure, the flange provided on the outer peripheral surface of the hub body becomes an obstacle, and the seal ring on the side of the flange can not be attached afterward. Accordingly, it is required that this seal ring be, before assembling the hub body and the outer ring together, fixedly fitted inside the side end of the outer ring. Then, it is necessary for the taper-rollers constituting the taper-roller bearing of the first row to be inserted into the hub body on the minor-diameter side of the outer ring while being kept in the state of being disposed along the inner peripheral surface of the outer ring. It might be required for smoothing this inserting operation that the taper-rollers do not shift on the minor-diameter side when performing the inserting operation. In the case of the prior art structure shown in FIG. 13, however, this problem does not occur, and therefore no contrivance against this problem is given.